Positive detenting ratchet



Aug 27, 1968 R.E.ARKQ "3,398,591

POSITIVE DETENTING RATCHET Filed April I. 1966 INVENTOR ROBERT E. ARKQ United States POSITIVE DETENTING RATCHET Robert E. Arko, Mount Prospect, Ill., assignor to Teletype Corporation, Skokie, 111., a corporation of Delaware Filed Apr. 7, 1966, Ser. No. 540,920

8 Claims. (Cl. 74142) ABSTRACT OF THE DISCLOSURE In the telegraph industry pawl and ratchet drives are commonly employed to rotate feed wheels which are in turn used to advance tapes, cards, etc. through various pieces of apparatus. Often detents are used in conjunction with such mechanisms to prevent the rotation. of the ratchet, and therefore the feed wheel, when the ratchet is not being rotated by the pawl. In some applications it is necessary to assure that, the, detent comes to rest between two teeth of the ratchet and not on top of a tooth.

Accordingly, an object of this invention is to provide a mechanism for assuring that the detent of a pawl and ratchet drive mechanism does not come to rest on top of a tooth of the ratchet.

A complete understanding of the invention may be had by referring to the following detailed description when taken in combination with the drawings wherein:

FIG. 1 is a front view of a pawl and ratchet drive mechanism employing the present invention and showing the detent correctly positioned;

FIG. 2 is a partial front view similar to FIG. 1 showing the detent incorrectly positioned; and

FIG. 3 is a partial front view similar to FIG. 2 showing the detent restored to its correct position.

Referring now to the drawing wherein like reference numerals designate like parts throughout the several views with particular reference being had to FIG. 1 there is shown a feed wheel 11 which is mounted on a shaft 12 and which has a plurality of pin-shaped teeth 13 for engagement with a perforated tape, card, etc. to advance it through a telegraph mechanism. Also fixed to the shaft 12 is a ratchet wheel 14 having a plurality of saw-tooth shaped teeth 15 which is used to rotate the feed wheel 11.

The ratchet wheel 14 is rotated by a pawl mechanism 16 comprised of a rocking lever 17 which is pivotally supported by a pin 18, a pawl 19 which is pivotally attached to the rocking lever 17 by a pin 20 and which is urged to rock counterclockwise with respect to the rocking lever 17 by a spring 21, and a yoke 22. The yoke 22 is mounted on an eccentric 23 which is in turn mounted on a sleeve 24.

The sleeve 24 is rotatably mounted on a constantly rotating shaft 25. A clutch (not shown) is provided for connecting the sleeve 24 to, and therefore causing it to rotate with, the shaft 25. This action causes the eccentric 23 to rotate which in turn causes the yoke 22 to oscillate in an up and down manner with respect to the shaft 25.

The yoke 22 is connected to the rocking lever 17 by a pin 26 so that oscillation of the yoke 22 causes the rocking lever 17 to rock up and down about the pin 18. When the lever 17 rocks upwardly the pawl 19 is moved upwardly by the lever 17. As the pawl 19 moves upwardly it is cammed outwardly by the sloping edge of one of the atent 3,398,591 Patented Aug. 27, 1968 teeth 15 of the ratchet wheel 14 against the action of the spring 21. As soon as the pawl 19 clears the sloping edge of a tooth 15 it is driven into engagement with the radial edge of the tooth by the spring 21.-Therefore, when the eccentric 23 drives the yoke 22 and the rocking lever 17 downwardly the pawl 19 forces the ratchet wheel. 14 to rotate clockwise by pulling the tooth 15 downwardly. This in turn causes the shaft 12 to be rotated and, therefore, causes feed wheel 11 to bev rotated so that a tape or card which is engaged with the teeth 13 of the feed wheel 11 will be advanced.

When the pawl 19 slides up the sloping edge of a tooth 15 it frictionally engages the outer edge of the ratchet wheel 14 and, therefore, urges the ratchet wheel 14 to rotate in a counterclockwise direction. counterclockwise rotation of the ratchet wheel 14 is prevented by a detent 27 comprised of a roller 28 which is rotatably mounted on a lever 29 that is in turn pivotally mounted on a pin 30. A spring 31 urges the lever 29 to rotate counterclockwise about the pin 30 and, therefore, drives the roller 28 into engagement with the teeth 15 of the ratchet wheel 14.

In normal operation the roller 28 engages two teeth 15 of the ratchet wheel 14, that is, the roller 28 engages the sloping side of one tooth 15 and the radial side of ithe next adjacent tooth. In this position the roller 28 prevents counterclockwise rotation of the ratchet wheel 14 by providing a force which must be overcome by the frictional force imparted to the wheel 14 by the pawl 19 if the wheel 14 is to be rotated during the upward movement of the pawl 19. The force imparted to the arm 29 by the spring 31 is chosen so that the amount of force necessary to cam the roller 28 out of engagement with the sloping side of one tooth and the radial side of an adjacent tooth is of such a magnitude that the frictional force imparted to the wheel 14 when the pawl 19 moves upwardly will not disengage the roller 28 from between two teeth of the ratchet 14 but so that when the pawl 19 moves downwardly the roller 28 will be disengaged from between two teeth 15 of the ratchet wheel 14.

The teeth 13 of the feed wheel 11 are positioned on the feed wheel 11 in such a manner that whenever the roller 28 is properly centered between two teeth 15 of the ratchet wheel 14, the teeth 13 of the feed wheel 11 are properly positioned with respect to the device through which the feed wheel 11 advances a tape, a card, etc. If, however, the roller 28 should come to rest on top of a tooth 15 the teeth 13 are improperly positioned with respect to such a device thereby resulting in damage to a tape, a card, etc. with which the teeth 13 of the feed wheel 11 are engaged. I

In order to prevent the roller 28 from coming to rest on top of a tooth 15 a positive detenting mechanism 32 is provided. The positive detenting mechanism 32 includes a lever 33 which is pivotally mounted on the pin 30 and which is urged to rotate clockwise with respect to the pin 30 by a spring 34 and an auxiliary pawl or lever 35 which is pivotally attached to the lever 33 by a pin 36 and which is urged to rock clockwise with respect to the lever 33 by a torsion spring 37.

Also attached to the lever 33 is a cam follower 38 which is supported by a pin 39. The cam follower 38 engages a cam 40 which is rotatably mounted on theshaft 12 by a bearing 41 and which is attached to a pulley 42. The pulley 42 is rotated by a large diameter pulley 43 through a belt 44. The large diameter pulley 43 is mounted on a sleeve (not shown) similar to the sleeve 24 which may be connected to the shaft 25 by means of a clutch (not shown) and which will thereupon rotate with the shaft 25 thus causing rotation of the large diameter pulley 43 and the pulley 42.

Rotation of the pulley 42 causes the cam follower 38 to move inwardly and outwardly with respect to the shaft 12.

This causes the lever 33 to rock back and forth about the pin 30 against and with the action of the spring 34. This in turn causes the auxiliary pawl 35 to move up and down with respect to the shaft 12 and, since the auxiliary pawl 35 is constantly urged to rock clockwise about the pin 36 by the spring 37, this causes the pawl 35 to move back and forth between the full-line position shown in FIG. 1 and the dotted line position also shown therein.

During normal operation the auxiliary pawl 35 simply slides on the teeth of the ratchet wheel 14 and does not affect the operation of the ratchet wheel 14 in any manner whatsoever. If, however, the roller 28 is positioned on top of a tooth 15, the tooth 15 with which the auxiliary pawl 35 is engaged is positioned in a lower position with respect to the auxiliary pawl 35 than it is when the roller 28 is properly centered between two teeth. This condition is shown in FIG. 2. Accordingly, when the auxiliary pawl 35 is caused to move up and down by the movement of the cam follower 38 its path of travel passes through the tooth 15 of the ratchet wheel 14 lying next adjacent the tooth 15 with which it is engaged. Because of this the auxiliary pawl 35 strikes the tooth of the ratchet Wheel 14 positioned adjacent the tooth with which it is engaged and imparts a slight clockwise rotational movement to the wheel 14. This moves the tooth 15 of the wheel 14 upon the top of which the roller 28 is positioned slightly to the left with respect to the roller 28 and thus allows the roller to fall between two of the teeth 15 of the wheel 14 thereby properly centering the ratchet wheel 14 and returning the teeth 13 of the feed wheel 11 to their proper position with respect to the apparatus through which the feed wheel 11 is advancing a tape, a card, etc. The total movement of the auxiliary pawl 35 after it engages a tooth 15 is of shorter length than distance between the teeth of the ratchet wheel 14 and, therefore, the pawl 35 does not rotate the wheel 14 through an entire step but merely positions the wheel with respect to the roller 28.

The relative sizes of the pulleys 42 and 43 are chosen with respect to the components of the pawl mechanism 16 so that the auxiliary pawl 35 oscillates at a high frequency with respect to the frequency of oscillation of the pawl mechanism 16 and with respect to the frequency of rotation of the ratchet wheel 14. For example, in one application it has been found desirable to rotate the pulley 42 approximately thirty times as fast as the ratchet is rotated. This assures that an improper positioning of the roller 28 on top of a tooth 15 will quickly be corrected thereby preventing damage to a tape, card, etc., with which the teeth 13 of the feed wheel 11 are engaged.

When the ratchet wheel 14 is rotated slightly by the auxiliary pawl 35 and the roller 28 becomes properly centered by the two teeth, the mechanism assumes the position shown in FIG. 3. The tooth 15 of the ratchet wheel 14 with which the auxiliary pawl 35 is engaged is then in a higher position with respect to the pawl 35 and, therefore, when the cam 40 moves the cam follower 38 in and out, the auxiliary pawl 35 follows a path which does not pass through any of the teeth of the ratchet wheel 14. Accordingly, further upward and downward movement of the auxiliary pawl 35 has no affect whatsoever on the positioning of the ratchet wheel. Thus it will be seen that the auxiliary pawl 35 acts to reposition the ratchet wheel 14, and therefore, the feed wheel 11, whenever the roller 28 is on top of a tooth 15 and has no affect on the apparatus at any other time.

Although only one embodiment of the invention is shown in the drawings and described in the foregoing specification, it will be understood that invention is not limited to the specific embodiment described, but is capable of modification and rearrangement and substitution of parts and elements without departing from the spirit of the invention.

What is claimed is:

1. A positive detenting device for a pawl and ratchet drive mechanism including:

a ratchet wheel having teeth;

a detent positioned in engagement with the teeth of the ratchet wheel for preventing rotation of the Wheel;

a pawl positioned adjacent the ratchet wheel in line with the teeth thereof for engaging a tooth of the ratchet wheel whenever the detent is engaged with the top of a tooth of the ratchet; and

means for moving the pawl into engagement with a tooth on the ratchet wheel when the :detent is positioned on top of a tooth of the ratchet wheel and then moving the pawl a distance less than the distance between two adjacent teeth on the ratchet wheel to disengage the detent from the top of a tooth of the ratchet wheel.

2. The positive deten-ting device according to claim 1 wherein the pawl is substantially always engaged with one of the teeth of the ratchet wheel and wherein the moving means slides the pawl on the tooth in a path passing through a tooth of the ratchet wheel other than the tooth with which the pawl is engaged when the detent is positioned on top of a tooth.

3. The :positive detenting device according to claim 2 wherein the moving means is a rotating cam which slides the pawl through the path at a high speed relative to the speed of rotation of the ratchet wheel.

4. In a drive mechanism wherein an oscillatable feed pawl engages and rotates a ratchet wheel at a predetermined frequency and wherein a detent engages the teeth of the ratchet to prevent rotation of the ratchet when it is disengaged from the pawl, the combination with the detent of:

means positioned for oscillating engagement with a tooth on the ratchet whenever the detent is positioned on top of a tooth; and

means for oscillating the tooth engaging means into engagement with a tooth and then through a path shorter than the distance between identical points on adjacent teeth of the ratchet at a frequency higher than the frequency at which the feed pawl engages and rotates the ratchet after the feed pawl has rotated the ratchet to assure that the detent is not positioned on top of a tooth of the ratchet.

5. The combination according to claim 4 wherein the tooth engaging means is an auxiliary pawl which is substantially always engaged with one of the teeth of the ratchet wheel and wherein the moving means oscillates the auxiliary pawl in a path which includes the tooth of ratchet wheel adjacent the tooth with which pawl is engaged when the detent is positioned on top of a tooth of the ratchet wheel and which is otherwise clear of the tooth on the ratchet wheel adjacent the tooth with which the auxiliary pawl is engaged.

6. A device for restoring rotatable members to a proper angular position whenever the rotatable members are angularly misaligned including:

a pawl,

means for guiding the pawl in a path including a portion of the rotatable member whenever the rotatable member is angularly misaligned and clearing the rotatable member whenever the rotatable member is in a proper angular position, and

means for constantly moving the pawl back and forth along the path.

7. The device according to claim 6 wherein the guiding means includes a-portion of the rotatable member so that the pawl rides .upon the rotatable member as it moves along the path.

8. The device according to claim 7 further including a pivot, a lever supported on the pivot and a spring; wherein the pawl is rotatably mounted on the lever and is driven into engagement with the rotatable member by the spring and wherein the lever is rocked about the pivot to move the pawl back and forth along the path.

(References on following page) References Cited UNITED STATES PATENTS James 235134 Richter 74-142 5 Christofi 74142 Bush.

Anderson et a1.

6 FOREIGN PATENTS 347,287 France. 576,293 5/ 1924 France. 1,275,053 9/ 1961 France.

FRED C. MATTERN, JR., Primary Examiner.

W. S. RATLIFF, Assistant Examiner. 

